It would be a nice feuture to use an othervise unusable cover (since hero is max cover upgraded) to level up the hero of that specific cover.
By using a cover for this, the hero could gain +1 level, or a fix amount of ISO increase, like 500 ISO. At least the iso-leveling-up progress bar would now make more sense 
At least, by this way, we would see less used heros leveled up, maybe some day we would even see a level 85 Bagman